1. Field of Invention
The present invention relates generally to the field of wireless communication and data networks. More particularly, in one exemplary aspect, the present invention is directed to methods and apparatus for flexible modes of operation in a transceiver.
2. Description of Related Technology
Wireless technology enables a plurality of user devices (e.g., mobile telephones, hand-held devices such as PDAs, or laptop computers) to communicate without wires, thereby enabling a wide variety of desirable applications leveraging improved mobility and convenience for the user. As is well known, wireless transceiver operation utilizes a radio and modem subsystem to propagate electromagnetic signals. Unfortunately, the transmission of radio waves over distances and through certain types of environments may require a considerable amount of electrical power at the transmitter, and in many wireless applications the proper management of energy resources is a design limitation (having implications in both physical energy storage, and rate of power consumption). Furthermore, for certain mobile applications requiring small form factor designs, the heat generated by radio system operation and inefficiency may be another design constraint. Such heat may need to be dissipated (via conduction, convection and/or radiation) in order to prevent component damage or degradation (e.g., shortening of its operational lifetime).
A wireless Local Area Network (LAN) or WLAN, such as for example one compliant with IEEE Std. 802.11 (“Wi-Fi™”), is one exemplary wireless application providing network access via spread-spectrum or Orthogonal Frequency Division Multiplexing (OFDM) modulation techniques. WLAN was originally designed for generic wireless local area networking and does not require any network infrastructure. WLAN could originally support simple network topologies, including peer-to-peer “ad hoc” networks. In such simple ad hoc networks, communication links may be established directly from one wireless device to another, without involving intermediate access points. WLAN installations are highly popular for a wide-ranging audience including everyone from home users and small businesses operators to large corporations and even city-wide publicly offered access. The ease of WLAN installation/operation, along with a large amount of market penetration, as well as a plethora of WLAN capable devices (e.g. laptops, smartphones, etc.) help ensure WLAN's future growth and continued popularity.
The antennas on WLAN devices are generally inefficient in comparison to other radio technologies, in large part due to space and cost considerations. Furthermore, many WLAN end devices have form factor and usability requirements which additionally complicate antenna designs (such as removable PCMCIA cards). The ad hoc networking feature of WLAN transceivers, and wide variation in transceiver quality, creates unique radio design and coordination issues. In a typical WLAN operation, a considerable amount of power is consumed by the radio interface even within a small area. This relatively large power consumption is needed to improve wireless packet reception/transmission (i.e., reduce or substantially eliminate bit errors or required retransmissions) with nearby transceivers which may have disabilities such as poor sensitivity or antenna isolation, geographically-induced issues such as Rayleigh fading, etc.
WLAN power distributions have held generally stable over the years since adoption of the technology. High-end radio vendors have generally used silicon advances to improve performance rather than reduce power. The broad adoption of Orthogonal Frequency Division Multiplexing (OFDM) in 2003, and that of Multiple Input Multiple Output (MIMO) technologies in 2007, have kept active WLAN power levels above one Watt. The increased modulation and coding complexity foreseeable over the coming years suggests that in the near future, radios may be required to sustain more than three watts in real workloads.
This increased transceiver energy usage is accompanied by shrinking industrial designs. For example, first generation WLAN implementations (such as those manufactured by the Assignee hereof) were afforded the full volume of a PCMCIA card, while the current generation model (at the time of this writing) is a mere fraction of that space. As enclosures shrink, the radio module often moves closer to the surface, where energy dissipated as heat can be felt by users. At the same time, it becomes more difficult to fit a thermal solution to manage and distribute the heat effectively so as to avoid component damage (or initiation of a self-protection action such as a thermally-induced shutdown). Examples of thermal solutions include heat sinks, heat pipes, and fans. These may introduce significant cost, complexity, and even acoustic noise, all of which are undesirable.
Traditionally, the industrial design of consumer products specifies functional components prior to considerations of thermal management. Generally, desired features, form factor requirements, industrial design and components are considered first, while power behavior of components and resultant heat requirements are accepted and managed by designers. This style of design was recently changed to reflect the importance of thermal management. Newer approaches consider dynamic thermal constraints and “hot” components such as the CPU, memory controller, GPU, etc., and include methods to appropriately limit their energy dissipation. In one exemplary prior art system, a microcontroller continuously monitors thermal sensors sited throughout the system looking for temperature conditions that might affect user comfort or safety, as well as the correct operation of the components. The microcontroller notifies the operating system to adjust component performance in order to reduce energy dissipation, and thereby reduce thermal load This improved processing architecture enabled the design of smaller enclosures, while ensuring user and component safety.
U.S. Pat. No. 7,171,570 to Cox, et al. issued Jan. 30, 2007 and entitled “Method and apparatus for selectively increasing the operating speed of an electronic circuit” discloses a system that facilitates selectively increasing the operating frequency of an electronic circuit, such as a computer system. The system begins by operating in a low-power state with the frequency and voltage of the electronic circuit set to low levels. Upon recognizing the need for performance beyond the low power level, the electronic circuit enters the first-intermediate power state. In this first-intermediate power state, the frequency and voltage are set to first-intermediate levels. Upon recognizing the need for performance beyond the first-intermediate power state, the electronic circuit enters the maximum-sustainable power state. In this power state, the frequency and voltage are set to maximum sustainable levels. Upon recognizing the need for performance beyond the maximum-sustainable power state, the electronic circuit temporarily enters a boosted power state beyond the maximum-sustainable power state. In this boosted power state, the frequency and voltages are set to levels beyond the maximum sustainable levels. See also U.S. Pat. No. 7,340,622.
U.S. Pat. No. 7,240,223 to de Cesare, et al. issued Jul. 3, 2007 and entitled “Method and apparatus for dynamic power management in a processor system” discloses a dynamic power management system which includes an operating system (OS) that causes a processor to operate in one of multiple run states that have different performance and/or power dissipation levels. The OS selects the run state in response to processor information (e.g., processor load) being monitored by the OS. The OS can predict future states of the processor information based on sampled processor information. The OS can take an average of the predicted and actual samples for comparison with a threshold to select a run state. The OS can track the number of consecutive saturated samples that occur during a selected window of samples. The OS can predict future processor information samples based on the number of consecutive saturated samples. See also U.S. Pat. No. 7,302,595.
The relationship between computational performance and energy is well understood by those of ordinary skill. The relevant literature contains many studies of component frequency and voltage adjustments (often discussed together) to balance latency and throughput considerations with power requirements. Conceptually, clock frequency and logic switching are directly related to both energy dissipation and instruction cycle execution. Therefore, because adjustments are reasonably fine-grained, one can fractionally decrease CPU speed and see a corresponding decrease in power consumption. Gate count (i.e., the number of logic gates used to realize a particular silicon or other implementation of a processor design) can also significantly impact power consumption.
Digital radio operation in many ways is significantly less flexible than generalized computing power management techniques in the prior art. Unlike a computing platform, which is largely a closed system unto itself, a wireless transceiver must broadcast and receive signals to many other transceivers, and therefore must comply with generally agreed upon messaging and radio protocols, which have specific timing requirements. Furthermore, certain forms of channel coding (e.g. Viterbi coding, Turbo coding, Reed Solomon, etc.) operate on large data blocks, and cannot be scaled down arbitrarily.
One common current working assumption is that WLAN transceivers need only “on” and “off” power states in order to manage power consumption. For instance, the “Power Save” mode defined by IEEE Std. 802.11 assumes that the sole way to reduce power is to completely disable the receiver, in effect deafening the system. Furthermore, the emphasis in radio power management has been on the idle case in which no application traffic is offered. When there is traffic to be serviced, the radio chooses a performance state determined by prevailing RF conditions, and dissipates as much energy as needed to implement that operational state.
Various approaches to wireless power consumption control are evidenced in the prior art. For example, U.S. Pat. No. 6,795,419 to Parantainen, et al. issued Sep. 21, 2004 and entitled “Wireless Telecommunications System Using Multislot Channel Allocation for Multimedia Broadcast/Multicast Service” discloses a method for operating a wireless telecommunication system and for providing a Multimedia Broadcast/Multicast Service MBMS broadcast transmission from a network operator to a mobile station. A first step determines a minimum bit rate requirement to broadcast a MBMS message and a number of radio blocks per time period that are required to satisfy the bit rate requirement. A second step allocates the determined number of radio blocks in accordance with a multislot transmission technique, wherein a plurality of time slots are used per frame, such that the mobile station is provided with at least one idle radio block between two active MBMS transmission periods. The at least one idle radio block may occur between two active MBMS radio blocks. A third step transmits the determined radio block allocation to the mobile station. In the preferred embodiment the step of determining may include a consideration of radio channel conditions and a multislot class of the mobile station. In one embodiment the step of allocating attempts to maximize the number of idle radio blocks and the mobile station, during the idle radio block, performs at least one of entering a reduced power consumption mode of operation, or entering a neighbor channel measurement mode of operation. In another embodiment the step of allocating allocates radio blocks so as to complete the data transmission within the shortest period of time.
U.S. Pat. No. 6,930,981 to Gopalakrishnan, et al. issued Aug. 16, 2005 and entitled “Method for Data Rate Selection in a Wireless Communication System” discloses data rate determination in a system where the available power fraction and available Walsh codes in each active leg are dynamically changing over time. This method adapts the rate (modulation and coding) based on the combined resource (power & code space) levels seen at each cell. The method results in maximization of the rate supportable by each cell given their resource-constrained situation while meeting the constraints of target packet or frame error rate and orthogonality. Furthermore, improved fast cell selection by the mobile results due to this approach that is based on knowledge of combined resource (power & code space) levels across the cells in the active set.
U.S. Pat. No. 7,197,069 to Agazzi, et al. issued Mar. 27, 2007 and entitled “Multi-pair Gigabit Ethernet Transceiver Having Adaptive Disabling of Circuit Elements” discloses various systems and methods for providing high speed decoding, enhanced power reduction and clock domain partitioning for a multi-pair gigabit Ethernet transceiver. ISI compensation is partitioned into two stages; a first stage compensates ISI components induced by characteristics of a transmitter's partial response pulse shaping filter in a demodulator, a second stage compensates ISI components induced by characteristics of a multi-pair transmission channel in a Viterbi decoder. High speed decoding is accomplished by reducing the DFE depth by providing an input signal from a multiple decision feedback equalizer to the Viterbi based on a tail value and a subset of coefficient values received from a unit depth decision-feedback equalizer. Power reduction is accomplished by adaptively truncating active taps in the NEXT, FEXT and echo cancellation filters, or by disabling decoder circuitry portions, as channel response characteristics allow. A receive clock signal is generated such that it is synchronous in frequency with analog sampling clock signals and has a particular phase offset with respect to one of the sampling clock signals. This phase offset is adjusted such that system performance degradation due to coupling of switching noise from the digital sections to the analog sections is substantially minimized.
Despite the foregoing, the prior art fails to provide an adequate solution for dynamic thermal control of wireless transceivers. Unlike power or heat management in a digital processor, some state transitions within radio systems can be significantly more disruptive to the operation of the transceiver (and user experience) than others. Hence, a minimally disruptive yet effective scheme for selecting and invoking such state transitions is needed.
Such an improved solution should operate seamlessly and without adversely impacting user experience on existing radio apparatus, and that of other wireless devices.
Moreover, such dynamic thermal management would be operable without requiring undue modification to implementations already deployed.
To these ends, thermal management schemes should minimally support “standalone” operation, where a dynamically managed client modifies its behavior without requiring non-enabled neighboring clients to do so in return.
In another aspect, multiple clients, each enabled by the present invention, would also advantageously work cooperatively to optimize a given client's heat dissipation and radio access requirements.
Lastly, such improved apparatus and methods would enable the use of high-performance radios in aggressively small industrial designs. In one exemplary usage scenario, certain IEEE Std. 802.11-compliant transmit power amplifiers (e.g., those with output powers in the 23-24 dBm range), which are conventionally considered “too hot” for portable computers or small handheld devices, could be utilized on such small mobile devices, thereby potentially providing higher range and/or data service capability.